Extrusion fabrication is a known process that involves forcing material, generally aluminum or aluminum alloy under a combination of heat and pressure, so as to be flowable (normally referred to as a “billet”), through an extrusion die tool to form a product having a cross section that matches the extrusion profile of the die tool. Many manufacturing processes involve extrusion fabrication. For example, extrusion fabrication is widely used in the manufacture of flat, multi-cavity aluminum tubes, which are used for small heat exchanger components in air-conditioners, condensers, and radiators.
U.S. Pat. No. 6,176,153 B1 to Maier (“Maier”) discloses a current method known in the art for manufacturing extrusion die tools, and is incorporated herein by reference. FIG. 1 shows a flow diagram of the Maier method. As shown in FIG. 1, the method begins with cutting steel in Step 10 to form the desired extrusion die tool design. In Step 10, the extrusion die tool is machine cut in a series of sub-steps from annealed (i.e., non-hardened), hot-working steel on machinery well-known in the art, such as a lathe and/or a mill, into a semi-finished state. The semi-finished state refers to the extrusion die tool being cut into the general, desired shape but not being cut to its final dimensions. Thus, a certain amount of stock metal remains on the extrusion die tool after this cutting step and will have to be removed later on in the manufacturing process.
After the extrusion die tool is cut into its semi-finished state, the die tool is hardened for the first time in Step 20 using known hardening processes. After the extrusion die tool is hardened in Step 20, the die tool is finished to its final dimensions in Step 30. In Step 30, the stock metal left on the extrusion die tool from Step 10 is ground and cut off until the die tool is shaped to the desired final dimensions (i.e., the “finished state”). As a result of the hardening process of Step 20, the extrusion die tool cannot be easily cut on a lathe or a mill in Step 30. Rather, the extrusion die tool is finished in Step 30 by a process utilizing surface grinders, polishing machines, and electric discharge machines (“EDMs”). The Maier method involves the use of both a conventional EDM and a wire EDM to make all the necessary cuts to produce a finished die tool. It will be appreciated that due to the amount of cuts performed by a conventional EDM, the use of the conventional EDM is very time consuming and costly because it utilizes an electrode, such as a copper or graphite electrode, that must be replaced for each cycle of cuts in this process.
After the extrusion die tool is finished, the extrusion die tool is coated in Step 40 by the chemical vapor deposition (“CVD”) process described in Maier. As described in Maier, the extrusion die tool is coated at pre-determined locations with a wear resistant carbidic, nitridic, boridic, and/or oxidic-coating material. After the finished extrusion die tool is coated at the desired location(s), the die tool is rehardened in Step 50 by known hardening processes. On the Rockwell C-scale of hardness (“Rc”), the die tool is hardened to a hardness of about 46-50 Rc.
Each of the aforementioned steps is time consuming and expensive. The two hardening steps alone add two to four days worth of time onto the manufacturing process for extrusion die tools. Further, cutting an extrusion die tool into its semi-finished state and then finishing the die tool into its finished state require a large number of processing steps. As will be appreciated by one skilled in the art, the finishing step is time-consuming due to the fact the steel has already been hardened which increases the difficulty of making the finishing cuts. Any reduction in the time required to manufacture extrusion die tools can provide an extreme benefit to manufacturers of these tools. Thus, what is needed is a method that reduces the time and cost involved in manufacturing extrusion die tools.